Fifteen micron diameter carbonized microspheres (3M Co.) have been shown to display significant peripheral streaming in flow through the microvasculature of the Golden Hamster cheek pouch. The objective of the current study was to locate a microsphere that exhibited significant axial streaming. Golden hamsters were anesthetized, placed on a respirator, and a catheter passed through the carotid artery into the left ventricle. The cheek pouch was prepared for vital microscopy using a single membrane preparation. Two different types of microspheres were used: 1) 10 micron diameter carbonized microspheres (3M Co.) with specific gravity of 1.23 gm/3, larger pollen grains, with a specific gravity of 1.11. Each intracardiac injection consisted of 10 to the fifth power microspheres suspended in 0.1 ml of 0.9% saline. The flow of microspheres through the arterial vasculature was recorded by cine filming, and the data analyzed as previously reported. The distribution of the 10 micron diameter carbonized spheres is very similar to that previously found for 15 micron diameter carbonized microspheres, showing significant peripheral streaming. The pollen grains, however, do not exhibit this effect but rather show pronounced axial streaming. The intraluminal distribution of particles within the microvasculature can be a strong function of rather subtle partcle parameters among which surface charge appears to be important.